First Little Golden Books were started in 1981. Because a copyright does not mean when a book was printed someone could have pulled the copyright from the story with Wilkins art and used it later on a First Little Golden Book with June Goldsborough art when they reprinted. Without seeing the book I'd only be guessing. Since my copy like yours is a first and doesn't mention 1973 I can only assume it was an error in a later reprint or since I can only find one seller useing 1973 that it's a typo by the sellre for the copyrght renewal date of 1976. I compliment you on questioning what a seller is saying. You need to be smarter then most book dealers when collecting these types of books.
I'm new to this and am trying to identify the books I have. I have a First Little Golden Book - Busy Timmy, which I believe is a first edition because the letter sequence is A-J on the copyright page (Santi's guide says 1st letter on the left) and 1982. However when I do a book search on some book sellers websites they have this book for sale from 1973. When did they first start printing First Little Golden Books? Any help is much appreciated!